The subject matter disclosed herein relates to micromotor assemblies and, in particular, to micromotors with gearboxes operating in fluid environments.
The performance and reliability of a micromotor operating in a fluid environment can be adversely affected by the seepage of the fluid into the micromotor itself or into a gearbox attached to the micromotor. Fluid in the gearbox may substantially increase friction loading on the micromotor and correspondingly decrease the amount of torque available to drive an external load. Medical cardiac interventional procedures, such as real-time three-dimensional intra-cardiac echocardiography (4D ICE), for example, typically make use of a catheter-guided transducer array. The catheter also encloses a micromotor assembly for which it is desirable to avoid, or to mitigate, any additional functional loading resulting from the possible incursion of fluid into moving mechanical parts.
FIG. 1 shows an imaging catheter tip 10 for use in a conventional cardiac interventional procedure, such as exemplified, for example, in commonly-assigned U.S. Patent Application Publication No. US 2008/0097403. The imaging catheter tip 10 includes a micromotor 11 with an associated gearbox 13 such that the micromotor 11 can impart an oscillating motion to an imaging transducer 21, the oscillation occurring about an axis of a drive shaft 23 as indicated by rotation arrow 25.
As the imaging transducer 21 is oscillated, a plurality of transducer elements in the imaging transducer 21 are electronically phased to form an electronic image by generating a three-dimensional dataset which may be sent to an associated data processing system (not shown). The micromotor 11, the gearbox 13, and the imaging transducer 21 are typically enclosed in a catheter housing 27 for insertion into a patient's body. The catheter housing 27 also typically encloses electrical conductors (not shown) for providing power to the micromotor 11 and the imaging transducer 21, and for sending signals from the imaging transducer 21 to the data processing system.
An acoustic coupling fluid 29 may be provided inside the catheter housing 27 as a medium for coupling ultrasound energy between the imaging transducer array 21 and a fluid medium (not shown) external to the imaging catheter tip 10. Accordingly, the micromotor 11, the gearbox 13, and the imaging transducer 21 are typically disposed within the acoustic coupling fluid 29. Under some circumstances, the acoustic coupling fluid 29 may, over time, leak or diffuse into either or both the gearbox 13 and the micromotor 11, resulting in additional friction loading in the gearbox 13. This leakage typically occurs through a cylindrical gap 17 formed between a rotating gearbox flange 15 and a non-rotating gearbox housing 19.
Because the operating range of the micromotor 11 may be limited by design constraints, operational torque needs to be efficiently outputted from the gearbox 13 to oscillate the imaging transducer 21. That is, it may not be feasible to increase the power output of the micromotor 11 so as to overcome the additional friction loading in the gearbox 13 resulting from the possible influx of ambient fluid. Moreover, simply increasing drive power to overcome higher gearbox loading may result in excessive heat buildup in the micromotor 11 and thus not conform to thermal regulations, such as may be set by regulatory agencies.
What is needed is an improved device and method for sealing a micromotor with an associated gearbox operating in a fluid environment.